A herpes virus is a virus that infects great majority of adults potentially and chronically, and it has a possibility of being re-activated. Typical examples of herpes virus are a simple herpes virus (herpes-simplex virus:HSV) and chicken pox-herpes zoster virus (varicella-zoster virus:VZV) both of which hide out in a sensory ganglion, an Epstein-Barr virus (EBV), a cytomegalovirus (CMV) both of which hide out in the lymphocyte in blood, etc. There are many patients who suffer from a characteristic dermatitis inflammation and pain, both of which are caused by infection and re-activation of simple herpes virus or varicella-zoster virus, and a sharp pain sometimes turns into severe sharp pain.
Among others, varicella-zoster virus causes chicken pox at first-time infection, and it hides out in a sensory ganglion, and after that it will serve as herpes zoster by re-activation. The pathology of herpes zoster is not solved completely, but if an immunity function falls by fatigue, stress, cold, pulse treatment of steroid, administration of antineoplastic drug, an operation, autoimmune disease, etc., varicella-zoster virus which was under latent infection in the sensory ganglion are re-activated. Consequently, it is thought that many adjoining nerve cells are damaged, a varicella-zoster virus is transmitted through the peripheral nerve further increasing, it infects the outer skin cell of a rule skin division, and that a characteristic dermatitis condition and sharp pain are caused. A sharp pain that appears before dermatitis is called pre-pain of “herpes zoster pain”, and pain at the period of skin symptom is called “acute herpes sharp pain”.
Red spots, blisters or pustules are found in the acute term and further decomposition or ulcer are presented in case of the serious illness, and skin symptom sometimes extends to the rule nerve generally. Acute herpes sharp pain is considered to be caused by the inflammation of skin, peripheral nerve, nerve solution, a ganglion or spinal rear angle, and in cases, it causes such sharp pain that patients suffer from sleep obstacle and loss of appetite.
Then, although much of acute herpes sharp pain disappears with recovery of exanthemas, at the period of six months after the symptoms of herpes appear, sharp pain remains in 10 to 15% of cases even after the recovery of exanthemas, and these cases shift to post herpetic neuralgia (abbreviated to “PHN” hereinafter). PHN is the centripetal nerve interception sharp pain of irreversible and incurable disease resulting from the nerve denaturation after inflammation, and a dangerous factor of the shift is deeply related to the condition of 50 years-old or more, prodromal pain, and further degree of seriousness of the disease, namely the degree of nerve damage (nonpatent literature 1).
A prodromal pain of herpes zoster which appears after varicella-zoster virus infection and before expression of skin symptom, a pain of the acute herpes zoster which is an inflammatory pain of acute term of herpes zoster, a post herpetic neuralgia (PHN) of nerve pain after inflammation and an after-pain of herpes zoster which appears at shifting term from a pain of the acute herpes zoster to a post herpetic neuralgia are called together “zoster-associated pain”.
There are mostly burning pains, and unpleasant blunt pains like stabbing with a needle, being extracted or being bound. There are also pains close to muscular pain like stiff shoulder or lumbago, and the electrifying or torn-apart pains. With each case, the pains of these are intermingled and the character of pains also changes with progress. Cutaneous sensation of tactile sense, sense of pain and feeling of the warm and the cold decreases, and a sensitive sense called allodynia which induces sharp pain by slight touching is often caused.
PHN is said to one of the diseases with difficult medical treatment, and there is still no established cure that makes it disappear for a short period of time. Therefore, it is very important to perform a medical treatment to relief the pain during the acute term when nerve damage is reversible, and to prevent from the shift to PHN.
As a cure at the time of suffering from herpes zoster, the anti-virus treatment to varicella-zoster virus is effective first. Although mitigation of sharp pain is also expected by this medical treatment in addition to mitigation of skin condition and shortening of the disease period, the control effect of PHN shift is not proved (nonpatent literature 2). Moreover, although external application of steroid or non-steroid anti-inflammatory agent (NSAIDs) is used as relief-pain medical treatment at the acute term, the effect or preventive effect of shift to PHN is not expected. As a cure after having shifted to PHN, vitamin agents, non-narcotic analgesics, pyrine antipyretic analgesics, non-pyrine antipyretic analgesics, anti-depressants, anti-spasm agents, local anesthetic agents (external application, injection), narcotic analgesics, N-methyl-D-aspartate (NMDA) receptor antagonists, capsaicin ointment, beam medical treatment, thermo-therapy, iontophoresis, nerve solution block, ultra-short waves treatment, infrared irradiation treatment and laser irradiation treatment etc. are reported. However, there is no satisfactory cure, because there are problems of side effects; the effective case are restricted; there is a problem that prognosis is not settled, etc.
An object of the present invention is to provide a medical agent which treats pain originated from herpes virus, and is excellent in the effect and little in side effect.